1. Field of the Invention
The present invention relates to draft gears and, in particular, to an improved draft gear having a very high preload, and a very short travel for the absorption and dissipation of input forces.
2. Prior Art
Reduced-slack assemblies or systems typically include a device to cushion and absorb forces placed on the system during car operation. The cushioning and absorption of forces is always done in the buff direction and sometimes in the draft direction as well. While such devices have acceptable absorption capacities, they are often lacking in mechanisms which protect the device against over-solid conditions.
The present invention overcomes the disabilities of the prior art by providing a a draft gear having a very high preload, limited axial travel, high energy absorption in both buff and draft directions and spring package protection in over-solid situations.
In accordance with general draft gear design, the present invention includes a housing with a closed end and an open opposite end which is provided with an internal pocket area wherein are located tapered wear liners. A wedge is mounted for axial movement in the open end of the housing and is situated for direct application of draft or buff forces. Friction devices are positioned within the housing, between the wedge and the wear liners, to absorb through friction some of the energy created by the application of a force to the wedge. A spring seat is positioned between the friction devices and a spring package which can be either an elastomeric pad stack or steel spring group.
The friction devices of the draft gear design include two opposed friction shoes, each having a first flat angled surface or face in sliding engagement with a corresponding flat, angled surface or face on the wedge. The angled surface of each friction shoe and the corresponding angled surface on the wedge form a first selected angle with respect to the major axis of the draft gear housing. In a preferred form, each friction shoe also has a second flat, angled surface or face in engagement with one of two tapered wear liners, located in and at opposite sides of the open end of the draft gear housing whereby forming a second selected angle with respect to the major axis of the draft gear housing. In a preferred form, each friction shoe also has a third flat, angled surface or face in engagement with a flat angled face or surface formed on the spring seat. The individual third flat angled face of the shoe and the individual flat angled face on the spring seat form a third selected angle with respect to the major axis of the draft gear housing.
In the preferred embodiment of the invention, the first selected angle of the adjoining surfaces of the friction shoe and the wedge is about 40 degrees, plus or minus about 3 degrees, but as much as 5 degrees. The second selected angle of the adjoining surfaces of the friction shoe and the wear liner surface is about 5 degrees, plus about 3 degrees and minus about 2 degrees. The third selected angle of the adjoining surfaces of the friction shoe and the flat face formed in the spring seat is about 65 degrees, plus or minus about 3 degrees. As is appreciated, all of these angles are measured with respect to the major axis of the housing. An elastomeric pad stack comprises a plurality of concentric elastomeric springs which are made in accordance with U.S. Pat. Nos. 4,566,678 and 5,351,844, which are incorporated by reference herein, may be employed to absorb additional energy. A spring package comprising steel springs can also be employed as an alternative to the elastomeric pad stack.
Thus, an object of this invention is the provision of a draft gear for a reduced-slack drawbar assembly which fits in a standard pocket and has no more than about 25 mm of travel.
Another object of this invention is the provision of a draft gear for a reduced-slack drawbar assembly which absorbs energy in both the buff and draft directions and has a metal shell to protect the spring package, whether an elastomeric package or a steel spring group, in the over-solid condition.
An additional object of this invention is the provision of a draft gear for a reduced-slack drawbar assembly which includes a housing and a spring package that is subjected to a preload of about 30,000 lbs. to about 50,000 lbs., depending on whether steel coil springs or elastomeric pads are employed.